Optical emitter-detector pairs (photo-eye) are used for sensing obstructions on motorized door operators. The emitter half creates a beam of light that is pointed across the door opening. This beam is received by the optical detector along with all the other sources of ambient light in the room. Ambient light is cancelled out largely by switching the emitter at a frequency much higher than ambient sources, say 30-khz, and using a frequency filter in the detector.
Such emitter-receivers are well known and available complete with all associated frequency driver and frequency discrimination circuitry. They are commonly used in garage door operators for obstruction detection and as remote controls on televisions.
In the instant application if an obstacle is in the door opening it is expected that it will block the light beam received by the detector thereby ultimately closing a switch contact. With the contact closed the motor operator will either not-close if it is already open or stop closing and re-open.
One mechanical mounting option has the emitter mounted on the floor to one side of a door or gate opening, and the detector mounted on the floor on the opposite side of the opening. The photo-eye is thereby fixed or non-moving but protects the opening. Wires connect emitter to detector to motor operator and run around the opening to avoid the moving door or gate. Typically 100-feet of wire is required for connection of the system.
Another mechanical option has the emitter and detector fastened on opposite sides of the moving edge of the door or gate, traveling with it. Flexible wire, coil cord, or a rotary wire reel connects the moving photo-eye to a fixed motor operator. The most common form being the 2-conductor wire reel. In the spring loaded wire reel electrical contact is made from its rotating reel to its stationary body by means of conductive brushes and rings. Such brushes create electrical noise while rotating when they are new, and as they age or if they become dirty the noise takes the form of momentary electrical disconnection from the brush to the ring.
All photo-eye systems require power to operate and in return provide a signal in the form of a voltage, voltage pulses, or a contact closure. Therefore you might conclude that two wires would be required for supplying power and one or two more wires would be used for the signal. In actual practice two-conductor, unshielded, non-twisted wire is preferred by installers primarily because they only have two-conductor wire and two-conductor wire reels are more common than others. Whereupon the manufacturers of photo-eyes designed their units such that power and signal can be sent over the same two wires.
Photo-eye alignment signals are superimposed or modulated into its two power wires. The motor operator will not work if the signal from the photo-eye is missing and will end up in the fully open position, unable to close. This becomes a security issue in that the door or gate cannot close unless the safety system is bypassed. Troubleshooting such a system problem without the benefit of an oscilloscope is difficult because the alignment signal is mixed with the power. Some industrial high security operators use 4-wire photo-eyes to avoid the troubleshooting difficulties involved with two wire systems.
Residential garage door operators use a microprocessor to receive the pulses from the photo-eye and software to detect their loss. If such pulses are missing the motor operator will not close if it is already open or stop and re-open if it is closing. Therefore if the photo-eye system has a broken wire, a shorted wire, a defective component, is misaligned, has no power or if the beam is blocked the effect is the same, the door will not close. Troubleshooting is difficult, and failures common, such that a bypass has been devised. Holding down the pushbutton for more than 2-seconds will close the door even if the photo-eye beam is blocked. The button must be held down continuously until the door is fully closed or it will stop.
Industrial door and gate operators do not come with a photo-eye. Conditions of dirt or mud, process dust or muck, snow or ice may make an optical system impractical because their lenses need continuous cleaning. To this end industrial motorized operators come with just an electrical terminal for the attachment of any number of different safety systems. A simple contact closure at this terminal will stop the motor operator from closing if it is open and will reopen it if closing. This invention primarily addresses this type of motor operator when conditions favor to the use of a photo-eye safety system.
The industrial operators predominantly tend to use electromechanical relay logic instead of microprocessor or electronic logic. The reason is reliability related to environmental issues, and electrical noise. Environmentally an industrial motor operator will be hot, wet and dirty. Each time the industrial motor stops every electrical conductor and trace inside the electrical enclosure will be at ground zero to a huge radiated and conducted electromagnetic pulse. This is caused by the residual magnetic field energy left in the motors windings collapsing whenever the motor contactor opens. The motor is located outside of the electrical enclosure but its high voltage arc is formed across contacts located inside the enclosure as they open the motors magnetic field.
Industrial doors and gates are heavy. They are built with thick steel to stop a vehicle from pushing through them and a typical example might be 3,000-lbs and an unusual example might be 30,000-lbs, moving this heavy load by hand is kind of, tough. They protect areas that absolutely require security. It is therefore more important that these motor operators work than say your garage door at home. If a photo-eye system is used it must be able to be repaired easily and bypassed temporarily when necessary.